Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 29 Mar 2022 09:50:24 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Xianting Tian <xianting.tian@linux.alibaba.com>
Cc:     mst@redhat.com, jasowang@redhat.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] virtio_ring: add unlikely annotation for free descs
 check
Message-ID: <20220329075024.eoajm5ufrcfytug4@sgarzare-redhat>
References: <20220328105817.1028065-1-xianting.tian@linux.alibaba.com>
 <20220328105817.1028065-2-xianting.tian@linux.alibaba.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: <20220328105817.1028065-2-xianting.tian@linux.alibaba.com>
Precedence: bulk

On Mon, Mar 28, 2022 at 06:58:17PM +0800, Xianting Tian wrote:
>The 'if (vq->vq.num_free < descs_used)' check will almost always be false.
>
>Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>---
> drivers/virtio/virtio_ring.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
>diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>index d597fc0874ec..ab6d5f0cb579 100644
>--- a/drivers/virtio/virtio_ring.c
>+++ b/drivers/virtio/virtio_ring.c
>@@ -525,7 +525,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> 		descs_used = total_sg;
> 	}
>
>-	if (vq->vq.num_free < descs_used) {
>+	if (unlikely(vq->vq.num_free < descs_used)) {
> 		pr_debug("Can't add buf len %i - avail = %i\n",
> 			 descs_used, vq->vq.num_free);
> 		/* FIXME: for historical reasons, we force a notify here if
>-- 
>2.17.1
>